Design, Fabrication, and Preliminary Testing of a Laboratory Scale Batch Reactor for the Removal of Chromate Ions from Metal Plating Waste Water

Author : Apil, Ronnel S.
Major Adviser : Alcanzare, Edilberto A.
Committee Members : Acda, Reynaldo I.; Valencia, Sixto A.
Year : 1994
Month : October
Type : Thesis
Degree: BS
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A laboratory scale batch reactor was designed and fabricated for the removal of chromate ions from metal plating wastewater. The reactor was tested for its effectiveness in the treatment process and used to evaluate the order of chemical reactions and specific reaction rate constants.

A simulated waste, containing potassium dichromate solution at the typical hexavalent chromium concentration of 205 ppm was used. The exothermic treatment process involved two stages: one for the reduction of hexavalent chromium in the form of chromic acid to nontoxic trivalent chromium as chromium sulfate, and another for the conversion of chromium sulfate into chromium hydroxide precipitates by calcium hydroxide. A complete reaction was indicated by the presence of a pale green solution during reduction and the basification of the reduced solution to between pH 8.5 and 9 which precipitates the amphoteric chromium hydroxide.

The reactor was tested with an operating volume of 10 liters 25°C and atmospheric pressure. Analysis of reaction kinetic data yield specific preliminary reaction values rate of reaction constant of order equal to 2.48 and 2.13, and specific reaction rate constant of 9289.848 li1.48·mol-1.48·min-1 and 1485.417 li1.13·mol-1.19·min-1, for reduction and precipitation, respectively.

At maximum conversion, the resulting residual concentration of hexavalent chromium was 2.1216 x 10-3 mg/li. The limit for maximum allowable concentration of 5 x 10-2 mg/li was achieved with this value.

Heat transfer analysis showed that the reactor can be operated at cooling water flowrate of 1.2 ml/sec/.

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